Traditionally, wireless communication networks include a Base Transceiver Station (BTS) and a Mobile Station (MS), each of which include a single antenna. Problems with this traditional design include the limited power within the transmissions from the BTS to the MS, also known as downlink communications, and the difficulty in transmitting more than one downlink data stream concurrently.
In more recent wireless network designs, the BTS comprise two or more antennas in order to increase the power of downlink communication signals and to allow for easier transmission of more than one downlink data stream concurrently. To accomplish this with minimal errors and maximum power, an orthogonal space-time encoding matrix is utilized that dictates the transmission for each of the antennas for a series of time periods. For instance, the following matrix:          [                            a                          b                                      c                          d                      ]  indicates that “b” and “d” should be transmitted by first and second antennas respectfully at a first time period while “a” and “c” should be transmitted by the first and second antennas respectfully at a second time period.
One well-known space-time matrix S for the case that a BTS with two antennas is transmitting first and second complex numbered data streams (x1, x2) is as follows:   S  =      [                                        x            2                                                x            1                                                            x            1            *                                                -                          x              2              *                                            ]  In this case, a transmitter coupled to a first antenna transmits x1 at a first time period and transmits x2 at a second time period. As well, a second transmitter coupled to a second antenna transmits −x2* at the first time period and transmits x1* at the second time period. It is noted that this matrix S is an orthogonal matrix which follows the property of:S·ST=I
Another well-known space-time matrix S for the case that a BTS with four antennas is transmitting first, second and third complex numbered data streams (x1,x2,x3) is disclosed in a published paper entitled “Space-Time Block Coding for Wireless Communications: Performance Results” by Tarokh et al., published in the IEEE Journal on Selected Areas in Communications, Vol. 17, No. 3, March 1999. In this well-known implementation, the space-time matrix (with slight formatting changes) is as follows:   S  =      [                                                      x              3              *                                      2                                                                          x              3              *                                      2                                                            -                          x              2              *                                                            x            1                                                                          -                              x                3                *                                                    2                                                                          x              3              *                                      2                                                            x            1            *                                                x            2                                                                          (                                                x                  2                                +                                  x                  2                  *                                +                                  x                  1                                -                                  x                  1                  *                                            )                        2                                                              (                                                -                                      x                    2                                                  +                                  x                  2                  *                                -                                  x                  1                                -                                  x                  1                  *                                            )                        2                                                              x              3                                      2                                                                          x              3                                      2                                                                                      -                              (                                                      x                    2                                    -                                      x                    2                    *                                    +                                      x                    1                                    +                                      x                    1                    *                                                  )                                      2                                                              (                                                -                                      x                    2                                                  -                                  x                  2                  *                                +                                  x                  1                                -                                  x                  1                  *                                            )                        2                                                              -                              x                3                                                    2                                                                          x              3                                      2                                            ]  In this case, four transmitters coupled to four antennas (represented by the rows in the matrix) transmit different expressions of the data streams at four different time periods (represented by the columns in the matrix, the far right column being the earliest time period).
One key problem with this system of using orthogonal space-time encoding matrices is that they do not allow the MS to scale easily to BTSs with varying numbers of antennas. In particular, a MS must be able to decode the data being received no matter what the number of antennas are at the BTS and, therefore, a separate space-time decoder must be included in each MS for the case that the BTS has two antennas, three antennas, four antennas, etc. This adds considerable additional elements to the MS and therefore increases the financial and space costs.